1. Field of the invention.
The field of the invention relates to the manufacture of footwear having a soft insole and an outsole provided with a cavity for receiving a cushion.
2. Brief description of the prior art.
The manufacture of footwear has involved a number of different processes depending upon the final product which is desired. There are, for example, three basic methods of outsole attachment: cementing, molding, and sewing. Cemented footwear includes any shoe in which the outsole is held in place by means of cement. One type of sole attached by the cement process is known as the "unit sole". A unit sole has generally been defined as an entire sole and heel construction that is molded separately as a single unit. A mold is closed to define a cavity having a desired shape and a soling compound is injected into the cavity. After the unit has been removed from the mold, it may be attached to an upper by the cement process. U.S. Pat. No. 2,995,840 provides an example of a unit sole made by a molding process.
Injection molded shoes are manufactured by placing an assembled upper in position in the loading station of the molding machine, closing the mold, and forcing a soling compound into a cavity formed between the bottom of the mold and the shoe bottom. The process lends itself to the production of casual footwear.
There are a number of sewing processes which are well known to the art for attaching an outsole. Many dress and work shoes today have a welted construction where the outsole is stitched to a welt. Shoes of cemented construction generally suffer a disadvantage compared to those of welt construction in that there is not enough room between the insole and the outsole for an adequate cushioning material. The unit sole is made of the same material throughout its thickness, and this material must be selected more for its wear resistance than its cushioning effect, especially in dress shoes with light weight edges.
A further disadvantage of the present process for manufacturing cement construction unit soled shoes is that the insole must be made of material that is too firm and stiff for good comfort. This firmness and stiffness are needed to withstand various machine lasting operations without buckling, wrinkling, or moving out of position. Hot melt machine lasting operations are by their very nature fast and forceful as they wipe the taut leather into place against the insole. It is not practical to hold the insole in place with tacks out near the edges, because the tacks would be covered by the lasted over upper, and exceedingly dangerous to the wearer if not removed. As a result, the tacks that temporarily hold the insole must be near the middle, increasing the need for stiffness in the insole. Often cement construction insoles are molded into a shallow compound shape to fit the bottom of the last, and firmness and stiffness are also required to hold the molded shape.
Attempts have been made to temporarily secure a stiffening material to a relatively soft insole by means of LATEX or rubber cement. While this will enable the insole to withstand the lasting process, difficulty has been experienced in removing the stiffener after lasting.